In recent years, due to the continuous reduction of petroleum and coal resource and the increasingly serious environmental pollution problems, the polymer materials industry which greatly depends on petroleum chemical industry is facing serious challenges. It is the most effective way to study green and renewable biomass material to replace petrochemical raw materials.
Biomass has the advantage of renewable, large annual production and wide distribution, but so far its utilization is very inefficient. How to efficiently convert renewable biomass resources into useful polymer materials has attracted great attention and interest from the whole world. Up to now, some biomass-based thermoplastics, such as polylactic acid, polyhydroxyalkanoate and the like, have been successfully synthesized and commercialized. However, there are few studies on biomass thermosetting resins compared to the rapid development of biomass thermoplastics.
Thermosetting resin is a kind of crosslinked polymer material with network structure, which has outstanding advantages such as superior strength, high heat resistance, good chemical resistance and excellent processability. It is widely used in coating, adhesives, electronic information and high performance composites and other fields.
Among the existing thermosetting resins, epoxy resin is widely used due to its excellent performance and low cost, accounting for about 70% of the thermosetting resin market, among which more than 90% is bisphenol A epoxy resin (DGEBA). The monomer of DGEBA is synthesized by bisphenol A and epichlorohydrin, both of which are based on petroleum and coal resources, under the condition of sodium hydroxide. Bisphenol A has a similar structure with estrogen, which reduces the fertility and is closely related to the increased risks of diseases and cancers. The US Federal Drug Administration has banned bisphenol A-based materials for packaging infant formula. Although the effects of bisphenol A on the endocrine system are still under study, the potential risks have led to the demand for bisphenol A-free products. At the same time, as bisphenol A is derived from petroleum and coal resources, under the premise of the continuous reduction of petroleum and coal resources, it is an urgent need for green renewable biomass epoxy resin raw materials to reduce the dependence of epoxy resin production on petroleum and coal resources.
In recent years, the literature reports on some biomass materials that replace DGEBA, such as vegetable oil, cardanol, itaconic acid, lignin and its derivatives. However, the biomass content of the synthesized epoxy resin cannot reach 100%, while there are shortcomings such as low reactivity of the epoxy resin system, poor mechanical properties of cured products, low glass transition temperature (Tg) and poor processability. Therefore, it is of great value to find an epoxy resin with high biomass content as well as excellent performance and its synthesis method.
Most of the biomass materials widely existed in nature is aliphatic compounds, which have poor thermal property. Therefore, eugenol and 2,5-furandicarboxylic acid stand out for their excellent thermal stability owing to their aromatic structure. 2,5-furandicarboxylic acid is listed as the top ten green chemical substances by U.S. Department of Energy. It is obtained by oxidation of 5-hydroxymethylfurfural (HMF), which can be obtained by dehydration of biomass-based C6 carbohydrates such as glucose, starch, cellulose and the like. Eugenol, accounting for about 80% of clove oil, is a renewable, low-toxic and relatively low-cost biomass material. Zhang et al. reported an epoxy resin based on eugenol with a biomass content of 62.7% (Ref: Jianglei Qin, Hongzhi Liu, Pei Zhang, Michael Wolcott and Jinwen Zhang. Polymer International, 2014, 63, 760-765). The cured product, prepared by using hexahydrophthalic anhydride as an epoxy curing agent, obtains a glass transition temperature (Tg) of only 114° C. Liu et al. reported an epoxy resin based on 2,5-furandicarboxylic acid (Ref: Jun Deng, Xiaoqing Liu, Chao Li, Yanhua Jiang and Jin Zhu. RSC advance, 2015, 5, 15930-15939), the cured product, taking hexahydrophthalic anhydride as a curing agent, has a Tg value of 152° C., but its biomass content is only 65.2%. These studies indicate that the existing study on the use of biobased materials to synthesize epoxy resins cannot simultaneously have the properties of full biomass (100%), high thermal performance and high mechanical properties. This is because the raw materials for synthesizing epoxy resin in the prior art are not all biomass materials, resulting in that the biomass content of the synthetic resin is not high, and the selected materials do not have good thermal properties and the like.